This is a reland of 96f55796
Original change's description:
> [test] Add test runner system tests for flaky tests
>
> This uses a temporary file in the mocked d8 script to let d8 flip
> between FAIL and PASS on rerun.
>
> This adds a separate test root with dedicated test suite for testing
> flakes to no interfere with existing status file configs.
>
> NOTRY=true
>
> Bug: v8:6917
> Change-Id: Id43753650195fb74cceb2a3ee9014100cabad546
> Reviewed-on: https://chromium-review.googlesource.com/867917
> Commit-Queue: Michael Achenbach <machenbach@chromium.org>
> Reviewed-by: Sergiy Byelozyorov <sergiyb@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#50621}

TBR=sergiyb@chromium.org
NOTRY=true

Bug: v8:6917
Change-Id: I4e7bca272dfd8778fbb8d012fcd6fd8406158e43
Reviewed-on: https://chromium-review.googlesource.com/868433Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50625}